In which case change in entropy is negative?

Under isothermal condition, a gas at 300 K expands from 0.1 L to 0.25 L against a constant external pressure of 2 bar. The work done by the gas is [Given that 1 L bar = 100 J]

The bond dissociation energies of X₂ , Y₂ and XY are in the ratio of 1 : 0.5 : 1. $$\Delta $$H for the formation of XY is –200 kJ mol^–1. The bond dissociation energy of X₂ will be

A gas is allowed to expand in a well insulated container against a constant external pressure of 2.5 atm from an initial volume of 2.50 L to a final volume of 4.50 L. The change in internal energy $$\Delta $$U of the gas in joules will be